Bare Knuckle Pickups Forum

Forum Ringside => Guitars, Amps and Effects => Topic started by: sgmypod on September 04, 2008, 07:31:15 PM

Title: Pulling valves
Post by: sgmypod on September 04, 2008, 07:31:15 PM
Have this 100pa monster head....is it possible to reduce power by pulling valves and if so do you also adjust ohmage of output(IE 4 valves 16ohm is 8ohm in 2)
Title: Re: Pulling valves
Post by: Woogie on September 04, 2008, 07:43:22 PM
Would the ohmage even change? Cos the speakers are the same.

Title: Re: Pulling valves
Post by: FELINEGUITARS on September 04, 2008, 08:21:14 PM
ohmage will change if you pull some valves even the though the speakers are the same
Title: Re: Pulling valves
Post by: sgmypod on September 04, 2008, 08:22:13 PM
I thought that...but will it kill amp or change biasing
Title: Re: Pulling valves
Post by: Roobubba on September 04, 2008, 08:36:35 PM
Of all people, I wasn't expecting Feline to use the "word" 'ohmage'...
Title: Re: Pulling valves
Post by: sgmypod on September 04, 2008, 08:37:17 PM
*L*
Title: Re: Pulling valves
Post by: Will on September 04, 2008, 08:42:14 PM
Of all people, I wasn't expecting Feline to use the "word" 'ohmage'...

I don't get it :?

Yeah, speakers take the load that the amp gives, half the power output, half the load the amp gives I think
Title: Re: Pulling valves
Post by: FELINEGUITARS on September 04, 2008, 10:56:09 PM
Yeah - halve the output impedance setting
Title: Re: Pulling valves
Post by: Oli on September 04, 2008, 11:03:06 PM
On one side of the transformer (the primary), you have the output section of the amplifier, and on the secondary coils, you have the speakers. Transformers work on a ratio system, so what happens on one side has to happen on the other- or else you end up with an imbalance, and mismatched impedance. By removing two of the valves from the power section, you halve the impedance, so you need to half the impedance on the speaker-side of things.
Title: Re: Pulling valves
Post by: Roobubba on September 05, 2008, 07:50:11 AM
Yay, Baby Jesus no longer needs to cry :)

Roo
Title: Re: Pulling valves
Post by: sgmypod on September 05, 2008, 02:33:39 PM
So 8ohm in 4valve(that I have set now on back) is now is 4ohm  when I remove 2 valves
Title: Re: Pulling valves
Post by: MrBump on September 05, 2008, 09:58:18 PM
I'm out of my comfort zone with all this valve stuff, but are we SURE that dropping valves changes "ohmage" (to quote Johathan)?

Doesn't it depend more on the output transformer?

I know ask because when John Cooper did work on my Orange and re-valved/biased it, he dropped 2 output valves, but the ohm setting remained the same.  I don't think that he did any other work.

Again, I don't know, but thems the facts, innit?

Mark.

Title: Re: Pulling valves
Post by: the_bleeding on September 06, 2008, 01:51:50 AM
dont pull valves. Sure it reduces wattage but it does NOT reduce volume by any noticeable amount. 3db is a very small difference for the risk you take doing it. Also, when you pull them, it makes your amp sound like shite. Your amp was designed for 4 valves, pulling 2 will make it sound gross. I have a halfpower switch on my amp, it effectively shuts off 2 valves. I relabeled it the "suck" switch because thats what it does.
Title: Re: Pulling valves
Post by: hamfist on September 06, 2008, 07:45:55 AM
dont pull valves. Sure it reduces wattage but it does NOT reduce volume by any noticeable amount. 3db is a very small difference for the risk you take doing it. Also, when you pull them, it makes your amp sound like shitee. Your amp was designed for 4 valves, pulling 2 will make it sound gross. I have a halfpower switch on my amp, it effectively shuts off 2 valves. I relabeled it the "suck" switch because thats what it does.

 This is a very common story to hear from people who have tried halving the number of output valves, although I admit I have not tried it myself.
Title: Re: Pulling valves
Post by: MrBump on September 06, 2008, 09:18:29 AM
dont pull valves. Sure it reduces wattage but it does NOT reduce volume by any noticeable amount. 3db is a very small difference for the risk you take doing it. Also, when you pull them, it makes your amp sound like shitee. Your amp was designed for 4 valves, pulling 2 will make it sound gross. I have a halfpower switch on my amp, it effectively shuts off 2 valves. I relabeled it the "suck" switch because thats what it does.

Hmmm...  I can't say I agree.  My Orange sounds amazing with just 2 EL34s.  Maybe it depends on the amp?

Mark.
Title: Re: Pulling valves
Post by: the_bleeding on September 06, 2008, 06:43:54 PM
Hmmm...  I can't say I agree.  My Orange sounds amazing with just 2 EL34s.  Maybe it depends on the amp?

Mark.

it most definately depends on the amp. But most often, pulling valves will give you bad tone. The best example i can think of is a peavey 5150. Holy cr@p it sounds bad when you pull em.... but its really sensitive to power tube changes.

You can always test ti and see if you like it, but dont get yer hopes up... (unless you have an orange :p)
Title: Re: Pulling valves
Post by: MrBump on September 06, 2008, 10:30:54 PM
(unless you have an orange :p)
!
damn right!!!

My Orange is from 1971, and is probably the least sophisticated bit of kit going.  Modern amps are going to have so much more going on that changing the circuit in that way will probably have a massive effect....
Title: Re: Pulling valves
Post by: sgmypod on September 06, 2008, 10:35:40 PM
Well this map ain't sophisticated think is a 70's..but well built